The proposed research will explore the core cognitive and neural mechanisms for maintaining precise mental representations over a few seconds in working memory. Current research indicates that imprecise working memory is a key cognitive dysfunction in mental illness, which may be responsible for a common complaint of ?brain fog? (e.g., blurry memory) from patients with mental disorders. Greater knowledge of the cognitive and neural mechanisms by which precise memory representations are maintained is pivotal not only to further our understanding of the overall architecture of the human mind in the healthy brain, but also to lay the groundwork for future clinical research on cognitive dysfunctions in mental disorders, including schizophrenia spectrum disorders. The research on working memory and its deficits in schizophrenia spectrum disorders in the past several decades has emphasized the quantitative aspect (capacity) of working memory and the corresponding neural mechanisms. However, only until recently has research begun to establish the theoretical and translational significance of the qualitative aspect (precision) of information maintained in working memory. The project will investigate the process and circuitry that support representing and retaining precise information in working memory using a combination of novel behavioral paradigms, individual differences, non-invasive brain stimulation, and functional magnetic resonance imaging. A novel cognitive and neural mechanism, namely pattern separation (Aim 2) in the hippocampal dentate gyrus subfield (Aim 3), is hypothesized to underlie mental clarity in working memory (Aim 1), based on the large literature on pattern separation and the emerging state model of memory that postulates a close relationship between short-term and long-term memories. The results will feed directly into our ongoing translational research (Aim 4) on foggy memory in schizophrenia spectrum disorders, including schizotypy (individuals at high risk for individuals at high-risk for psychosis symptoms). The present project will provide a clearer understanding of the functional limitations in working memory, which will establish the basic science backbone for future research designed to understand and treat cognitive dysfunction in schizophrenia spectrum disorders.